This invention relates to a fuel cell power generation system. More particularly, it relates to a favorable method of starting said system in which fuel is used directly as a heating medium for raising the temperature of said system.
Only a few cases have hitherto been known in which any description is made regarding the method of starting a fuel cell power generation system. For example, in "Description of a Generic 11-MW Fuel Cell Power Plant for Utility Applications" (EPRI EM-3161, Sept., 1983), which gives a typical example of investigation on a power generation system using a phosphoric acid type fuel cell, it is described regarding the start-up temperature elevation of a fuel reformer that "during start-up, the system is filled with nitrogen, and a start-up recycle compressor is operated such that nitrogen is circulated through a reformer and a heating system operated by means of a starting torch provided at the upper part of the reformer"; as to the start-up temperature elevation of the fuel cell, it is shown that said temperature elevation is effected by providing a heater in a cell-cooling system which is used as such in normal operation, heating the coolant water by means of the heater, and circulating the heated water.
The reformer is divided into a reaction part and a heating part, and the reaction part is packed with a catalyst for reforming. Therefore, inflow of an oxygen-containing gas to the reaction part should be avoided because it would poison the property of the catalyst. Accordingly, it has been general practice to use nitrogen, an inert gas, as the heating medium.
However, when nitrogen is used as a heating medium in the prior method, it causes an increase of the consumption of said nitrogen gas, and necessitates providing a nitrogen recycle system for start-up. Further, a process step is necessary to replace high-temperature nitrogen used in start-up with low-temperature fuel, which causes an increase of start-up time and necessitates a control system to suppress the pressure fluctuation in the fuel system.
Further, although the use of coolant water for raising the temperature of a fuel cell is practicable in a phosphoric acid type fuel cell, which operates at relatively low temperature (about 170.degree. to 210.degree. C.), an other method of temperature elevation is required for a molten carbonate type fuel cell, which can operate only at high temperature (about 400.degree. C. or above).